For an arithmetical sequence the first term is ... - JAMB Mathematics 1992 Question
For an arithmetical sequence, the first term is 2 and the common difference is 3. Find the sum of the first 11 terms
A
157
B
187
C
197
D
200
correct option: b
a = 2, d = 3 and n = 11
To find Sn/sub> = (\frac{n}{2}) [2a + (n - 1) (\delta)]
= (\frac{11}{2}) [2(2) + (11 - 1) 3]
= (\frac{11}{2})n [4 + 10(3)]
= (\frac{11}{2})(34)
= 11 x 17
= 187
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